The term cacogeusia comes from the Greek adjective kakos (bad, unpleasant) and the Latin noun gustum (taste). It translates as ‘bad taste’. It is used to denote a *gustatory hallucination or illusion presenting in the form of an unpleasant taste. Cacogeusia is often associated with – and confused with – *cacosmia. Etiologically, it is associated primarily with diseases of the tongue, oral cavity, oesophagus, and stomach, as well as with disorders of the upper respiratory tract. Cacogeusia may also occur as a side effect of recently ingested food, drinks, therapeutics, or illicit substances. In some cases it can be attributed to central disorders of the gustatory tract. Cacogeusia is classified as one of the *chemosensory disorders.